Journal
AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY
Volume 282, Issue 5, Pages H1717-H1723Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpheart.00899.2001
Keywords
baroreflex sensitivity; heart rate; nitroprusside; phenylephrine
Funding
- NHLBI NIH HHS [HL-61388, HL-10488] Funding Source: Medline
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The purpose of this project was to test the hypothesis that baroreceptor modulation of muscle sympathetic nerve activity (MSNA) and heart rate is altered during the cold pressor test. Ten subjects were exposed to a cold pressor test by immersing a hand in ice water for 3 min while arterial blood pressure, heart rate, and MSNA were recorded. During the second and third minute of the cold pressor test, blood pressure was lowered and then raised by intravenous bolus infusions of sodium nitroprusside and phenylephrine HCl, respectively. The slope of the relationship between MSNA and diastolic blood pressure was more negative (P < 0.005) during the cold pressor test (-244.9 +/- 26.3 units.beat(-1) . mmHg(-1)) when compared with control conditions (-138.8 +/- 18.6 units.beat(-1).mmHg(-1)), whereas no significant change in the slope of the relationship between heart rate and systolic blood pressure was observed. These data suggest that baroreceptors remain capable of modulating MSNA and heart rate during a cold pressor test; however, the sensitivity of baroreflex modulation of MSNA is elevated without altering the sensitivity of baroreflex control of heart rate.
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